<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var str1 = "hello";
        var str2 = "world";


        var result = str1.concat(str2);
        console.log(result);
        console.log(str1.concat(str2));

        var one = 1;
        var two = 2;
        var three = '3';


        ''.concat(one, two, three) // "123"

    </script>
</body>

</html>